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Miocene extension in the back arc of the retreating Hellenic subduction zone resulted in metamorphic core complex formation and exhumation of the Cycladic HP‐LT rocks. The extension was accommodated by bivergent detachment systems, generally occupying the interface between the Cycladic Blueschist Unit (CBU) and overlying Pelagonian units. However, the nature and kinematic history of the contact between the CBU and underlying Cycladic Basement (CB) in the southern Cyclades remains debated due to the presence of both top‐to‐the‐N and top‐to‐the‐S kinematics and ambiguities dating the final exhumation stages. Zircon and apatite (U‐Th)/He data and thermal modelling for the CB and CBU on Ios and Sikinos show that both units were likely exhumed as a coherent footwall block in response to rapid slip along the bivergent Miocene Santorini and Naxos‐Paros detachment systems. [ABSTRACT FROM AUTHOR]

The interplay between structural and metamorphic processes operating along the deep plate interface in subduction zones remains elusive as much of the geologic record is recycled into the mantle. In some cases, metamorphosed subducted rocks are underplated and exhumed to the surface, providing critical constraints on structural processes and the rheological evolution of subduction interfaces at convergent margins. One such exhumed high‐pressure/low‐temperature subduction complex is the Cenozoic Nevado‐Filábride Complex (NFC) in Southern Spain. This study presents new data from the NFC that elucidate the syn‐metamorphic deformation, stacking, and underplating of continental slivers along the subduction interface. The structurally lowest NFC dominantly comprises lithologically monotonous Paleozoic metamorphic basement rocks recorded by apatite U‐Pb ages and shows no evidence for large‐scale internal duplications suggesting it behaved as a coherent basement succession during subduction. In contrast, structurally higher levels of the NFC are characterized by the stacking of older‐on younger coherent slices and distinctly different metamorphic ages. These relationships document syn‐subduction structural repetitions and tectonic stacking of imbricate thin slivers (∼100s m) during subduction underplating. Structurally higher levels of the NFC exhibit both Eocene and Miocene metamorphic zircon rims and apatite ages, along with microstructures indicative of relatively higher temperature metamorphism. Large‐scale underplating and antiformal stacking of slivers in the subduction channel can provide buoyancy forces to underplate and assist exhumation. We demonstrate that the presubduction stratigraphic architecture is a key control on the style and timing of deformation and metamorphism, facilitating coherent subduction underplating. Plain Language Summary: Subduction zones are tectonic boundaries where one rigid lithospheric plate sinks underneath another. At the interface between the two plates, rocks experience intense temperature, pressure, and stress conditions during metamorphism, causing deformation. The geologic record of these processes is often not accessible unless these rocks return to the surface. Our study targets one such exposure in Southern Spain, the Nevado‐Filábride Complex, which records deformation and structural mixing from subduction and subsequent transfer to the overriding plate. We perform geochronologic analyses to determine the age of zircon overgrowths that reveal the timing of metamorphism. Additionally, we date apatite minerals and examine deformation relationships at the microscopic scale to approximate the temperature conditions that these rocks experienced. We synthesize these new results with previously established geochronology of zircon grains from the same region that collectively show evidence for the large‐scale structural stacking of coherent rock slivers during deformation. The stacking pattern is observed only in the weak upper stratigraphic successions, while the deeper unit remained internally intact and experienced a lesser degree of metamorphism. Our results argue that the style and distribution of deformation during subduction are strongly influenced by the original stratigraphic architecture and properties prior to subduction. Key Points: Two main Cenozoic metamorphic events were recorded in the Betic subduction zone in Eocene and Miocene by zircon and apatiteImbrication and thrust faults coeval with underplating developed along the subduction interfaceSubduction of thick coherent metamorphic basement enhances buoyancy forces and contributes to exhumation [ABSTRACT FROM AUTHOR]

During the Devonian, the Svalbard Archipelago lay at low latitudes, occupying a paleogeographic position at the intersection of Caledonian and Ellesmerian orogens. Provenance analysis, including detrital zircon U‐Pb age studies, of Devonian (ca. 420–360 Ma) strata from the Andrée Land Basin, Svalbard, help reconstruct sediment sources to understand the assembly of the three basement provinces that make up Svalbard, which are presently separated by Devonian sedimentary basins and(or) faults with syn‐to post‐Devonian displacement. The studied Andrée Land Group strata, which are part of the North Atlantic's Old Red Sandstone, consist of the Early Devonian Wood Bay Formation and Middle to Late Devonian Mimerdalen subgroup. Paleocurrent indicators from Lower to lower‐Middle Devonian strata record north‐directed sediment transport. Detrital zircon U‐Pb ages indicate a prominent "Caledonian" signal and include sources from Svalbard's Northwestern and(or) Southwestern basement provinces. In Middle and Upper Devonian strata, paleocurrents and detrital zircon ages record a shift to a predominantly eastern‐northeastern provenance, likely from the uplifting Ny‐Friesland block along the Billefjorden Fault Zone. Late Ediacaran‐early Cambrian detrital zircons in the uppermost Planteryggen Formation (Frasnian) indicate extrabasinal sources possibly associated with the Timanian orogen of Northern Baltica. The combined provenance data suggest Svalbard may have already been assembled, similar to the modern block, with the Andrée Land Basin located between modern exposures of the Southwestern/Northwestern and the Northeastern basement provinces. Comparison of detrital zircon ages from Andrée Land Group strata with those from other circum Arctic Devonian strata provides constraints on Svalbard's paleogeographic position in the Devonian. Key Points: Provenance analysis of the Andrée Land Basin identifies N‐NE paleodrainage in the Early Devonian and W‐SW in the Middle‐Late DevonianSvalbard's three basement provinces were likely juxtaposed into a relative position similar to the present day by the end of the DevonianDetrital zircon U‐Pb age comparisons of circum Arctic Devonian strata further constrain Svalbard's paleogeographic position in the Devonian [ABSTRACT FROM AUTHOR]

Sikinos and Ios Islands, located in the Southern Cyclades, represent part of a Cenozoic metamorphic core complex system that exposes subduction‐related metamorphic rocks in the highly extended back‐arc region of the Hellenic subduction zone. These exhumed HP‐LT metamorphic units are composed of Mesozoic metasedimentary rocks of the Cycladic Blueschist Unit (CBU) and the Paleozoic Cycladic Basement (CB). The magmatic and stratigraphic evolution of these units, as well as the nature of the contact between the CBU and CB, have remained poorly understood. We used zircon U‐Pb dating to determine crystallization ages of the CB on Sikinos and the maximum deposition ages and detrital provenance of the metasedimentary units to reconstruct the Mesozoic to early Cenozoic stratigraphic and tectonic evolution of the CBU on both islands. The results reveal that the CB in Sikinos is composed of Cambrian‐Silurian metasedimentary rocks intruded by Carboniferous granites and is overlain by metasedimentary rocks of the CBU with depositional ages spanning from Permo‐Triassic to Late Cretaceous. The provenance data from the CBU records a long‐lived tectonic evolution from Paleo‐Tethys subduction and rifting, to passive margin formation, and to subduction of the Neo‐Tethyan Pindos basin. The continuous stratigraphic record and provenance evolution from the CB into the CBU imply a para‐autochthonous relationship. On NE Sikinos and Ios, stratigraphic constraints suggest older‐over‐younger relationships along cryptic‐thrusts, supporting premetamorphic or synmetamorphic structural repetition of the CBU by imbrication, likely during subduction underplating. Key Points: Zircon U‐Pb analyses on Sikinos argue for a para‐autochthonous CB‐CBU contact and against an allochthonous contactDeposition of CBU is initially sourced in local synrift basins and transitions to passive continental margin and a cosmopolitan DZ spectrumMDAs from Sikinos and Ios reveal distinct tectono‐stratigraphic packages and thrust relationships within the CBU formed during subduction [ABSTRACT FROM AUTHOR]

The Cycladic Basement (CB) and the overlying Cycladic Blueschist Unit (CBU) are part of the Paleogene Cycladic subduction complex exposed in Miocene metamorphic core complexes in the distended back‐arc of the retreating Hellenic subduction zone of the southern Aegean. While the Cenozoic tectono‐metamorphic evolutions of the CB and the CBU have been the foci of numerous studies, this study presents new laser ablation inductively coupled plasma mass spectrometry bedrock and detrital zircon (DZ) U‐Pb ages that place robust constraints on the presubduction tectonic, magmatic, and paleogeographic evolution of the CB. Zircon U‐Pb ages of crystalline CB are ~306‐330 Ma, demonstrating local plutonism associated with regional voluminous, protracted Carboniferous magmatism related to Paleo‐Tethys subduction. The plutons intruded the CB metasedimentary host‐rock sequence, characterized by distinct Gondwanan DZ U‐Pb provenance, Neoproterozoic to early Paleozoic maximum depositional ages, and synmagmatic, contact metamorphic zircon rims (~300‐330 Ma). DZ U‐Pb dating revealed postmagmatic Permian metasedimentary rocks (~270‐295 Ma) that unconformably overlie the CB and have unimodal DZ spectra that indicate exhumation of the CB prior to Permian deposition within extensional basins, as well as mark the onset of CBU deposition prior to formation of the Pindos rift domain. These U‐Pb results clarify the late Paleozoic‐early Mesozoic evolution of the CB as a peri‐Gondwanan terrane composed of Neoproterozoic and early Paleozoic metasedimentary rocks, intruded by voluminous Carboniferous arc magmatism, and exhumed in the Permian, prior to Triassic rifting and CBU deposition. Additionally, these data provide a chronostratigraphic framework and illuminate subduction‐related juxtaposition within the CB metasedimentary sequence. Key Points: The Cycladic Basement consists of 330‐305 Ma granitoids hosted by Neoproterozoic‐Carboniferous paragneisses with peri‐Gondwanan affinityPermian paragneisses record the earliest deposition of the Cycladic Blueschist Unit prior to the rifting of the Neo‐Tethyan marginThe Basement stratigraphic evolution may indicate thrust juxtaposition of this continental fragment within the Eocene subduction zone [ABSTRACT FROM AUTHOR]

Detailed mapping and structural observations on the Cycladic Blueschist Unit (CBU) on Iraklia Island integrated with detrital zircon (DZ) U-Pb ages elucidate the Mesozoic pre-subduction and the Cenozoic orogenic evolution. Iraklia tectonostratigraphy includes a heterogeneous Lower Schist Fm., juxtaposed against a Marble Fm. and an overlying Upper Schist Fm. The contact is an extensional ductile-to-brittle-ductile, top-to-N shear zone, kinematically associated with the Oligo-Miocene exhumation. The DZ spectra of the Lower Schist have Gondwanan/peri-Gondwanan provenance signatures and point to Late Triassic Maximum Depositional Ages (MDAs). A quartz-rich schist lens yielded Precambrian DZ ages exclusively and is interpreted as part of the pre-Variscan metasedimentary Cycladic Basement, equivalent to schists of the Ios Island core. The Upper Schist represents a distinctly different stratigraphic package with late Cretaceous MDAs and dominance of Late Paleozoic DZ ages, suggestive of a more internal Pelagonian source. The contrast in the DZ U-Pb record between Lower and Upper Schist likely reflects the difference between a Paleotethyan and Neotethyan geodynamic imprint. The Triassic DZ input from eroded volcanic material is related to the final Paleotethys closure and Pindos/CBU rift basin opening, while late Cretaceous metamorphic/magmatic zircons and ~48–56 Ma zircon rims constrain the onset of Neotethyan convergence and high-pressure subduction metamorphism. [ABSTRACT FROM AUTHOR]